electricalperson
Senior Member
- Location
- massachusetts
gfci's dont need an equipment ground to operate. they work by sensing a current unbalance.
GFCI's do not need an EGC (moved from another thread)
- Thread starter quogueelectric
- Start date
- Status
76nemo
Senior Member
- Location
- Ogdensburg, NY
Holy smokes
Holy smokes
Something has to give. Shoot, I thought this would of been locked by now. It sounds like to me, here's where everyone changes to a different topic:grin: , that quogue understands it's operation. It is a possibility that the testing function is and the installation function is causing a great deal of unnecessary bickering here.
#1 No grounding wire is needed for the GFCI to properly operate, it senses the balance between ungrounded and the grounded, hence hot and neutral. Like that hasn't been explained in the last three pages, eh
#2, and I think this is where the confusion may lie, (you're either with me or not quogue), the GFCI device must have a ground in order to be tested with an EXTERNAL tester. The test button will work w/o a ground, but with an EXTERNAL tester, a ground must be present in order for YOUR tester to open the circuit.
Nowww, let's moooooooove on:grin:
Holy smokes
Something has to give. Shoot, I thought this would of been locked by now. It sounds like to me, here's where everyone changes to a different topic:grin: , that quogue understands it's operation. It is a possibility that the testing function is and the installation function is causing a great deal of unnecessary bickering here.
#1 No grounding wire is needed for the GFCI to properly operate, it senses the balance between ungrounded and the grounded, hence hot and neutral. Like that hasn't been explained in the last three pages, eh
#2, and I think this is where the confusion may lie, (you're either with me or not quogue), the GFCI device must have a ground in order to be tested with an EXTERNAL tester. The test button will work w/o a ground, but with an EXTERNAL tester, a ground must be present in order for YOUR tester to open the circuit.
Nowww, let's moooooooove on:grin:
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
080720-1351
The internal circuit for a GFCI is shown in the National Semiconductor datasheet:
http://cache.national.com/ds/LM/LM1851.pdf
Note: a current transformer is used to measure the differential current between hot and neutral, and power to operate the circuit comes from hot to neutral. There is no functional need for an EGC to operate the GFCI. Connection of the EGC or not to the GFCI will have no effect on the operation of the GFCI.
Also note: the trip time curve per UL943 requires tripping at 5 ma within 7 seconds, this is quite long. You will get a very good shock before a unit that trips on the UL limit curve opens.
In a sense GFCI is the wrong name for this device because it is not necessary for the current to flow to or thru ground. A current from any source that produces a difference in the hot relative to neutral currents will cause the GFCI to trip. It is not necessary that the current path be thru the EGC. In other words you do not need to have a shunt current to the EGC to trip the device.
.
The internal circuit for a GFCI is shown in the National Semiconductor datasheet:
http://cache.national.com/ds/LM/LM1851.pdf
Note: a current transformer is used to measure the differential current between hot and neutral, and power to operate the circuit comes from hot to neutral. There is no functional need for an EGC to operate the GFCI. Connection of the EGC or not to the GFCI will have no effect on the operation of the GFCI.
Also note: the trip time curve per UL943 requires tripping at 5 ma within 7 seconds, this is quite long. You will get a very good shock before a unit that trips on the UL limit curve opens.
In a sense GFCI is the wrong name for this device because it is not necessary for the current to flow to or thru ground. A current from any source that produces a difference in the hot relative to neutral currents will cause the GFCI to trip. It is not necessary that the current path be thru the EGC. In other words you do not need to have a shunt current to the EGC to trip the device.
.
chris kennedy
Senior Member
- Location
- Miami Fla.
- Occupation
- 60 yr old tool twisting electrician
Do you have an example aside from the noise mentioned in you link?gar said:
BTW, cool link gar, saved that one.:smile:
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
080720-1555 EST
Chris:
Here is a simple example of how to get an unbalanced current into the output side of the GFCI.
10 MA at 120 V is produced with a resistance of 120/0.01 = 12,000 ohms. Use a 2 W resistor. Connect one end of the 12,000 resistor from the hot input wire going into the GFCI the other resistor end to the neutral output slot of the GFCI. This provides and unbalanced 10 MA current thru the GFCI and does not produce any current in the EGC wire.
Go to the hot output slot and the GFCI should not trip. Same between input neutral and output neutral.
Put this same resistor between the two output slots of the GFCI and nothing should happen.
.
Chris:
Here is a simple example of how to get an unbalanced current into the output side of the GFCI.
10 MA at 120 V is produced with a resistance of 120/0.01 = 12,000 ohms. Use a 2 W resistor. Connect one end of the 12,000 resistor from the hot input wire going into the GFCI the other resistor end to the neutral output slot of the GFCI. This provides and unbalanced 10 MA current thru the GFCI and does not produce any current in the EGC wire.
Go to the hot output slot and the GFCI should not trip. Same between input neutral and output neutral.
Put this same resistor between the two output slots of the GFCI and nothing should happen.
.
crossman
Senior Member
- Location
- Southeast Texas
More examples of what GAR mentions:
GFCI receptacle connected to "A" phase. Connect a load between the "hot" slot and a "B" phase conductor.
GFCI receptacle connected to "A" phase. Connect a load between the "neutral" slot and a "B" phase conductor.
GFCI receptacle connected to "A" phase. Connect a load between the "hot" slot and a "B" phase conductor.
GFCI receptacle connected to "A" phase. Connect a load between the "neutral" slot and a "B" phase conductor.
chris kennedy
Senior Member
- Location
- Miami Fla.
- Occupation
- 60 yr old tool twisting electrician
Thank you both Gary and gar. I can think of lots of ways to trip a GFCI. gars post led me to believe there were real life application where this imbalance would occur.
stickboy1375
Senior Member
- Location
- Litchfield, CT
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
chris kennedy said:
A neutral to neutral connection between two circuits downstream of the GFCI, or a hot to hot connection of two circuits on the same phase (again downstream of the GFCI) can cause imbalance current to flow and trip the GFCI.
This sort of circuit to circuit fault will not cause excessive current flow, and probably won't trip an ordinary breaker. However this sort of circuit to circuit fault is getting detected quite frequently now that AFCI breakers are being installed.
(AFCIs have a ground fault detection component to their operation, and in addition to detecting arc faults they also will detect current imbalance. They are not as sensitive to such current imbalance as GFCIs, but I believe that they will trip on 70mA of imbalance.)
-Jon
76nemo said:
This was my thought exactly as I was reading through the thread.
Take a standard, 3-wire GFI plug in tester and stick it into a non-grounded GFI-protected receptacle. The tester WILL NOT TRIP the GFI. And I agree with 76 here... I think that is where the misconception comes from.
- Location
- Massachusetts
480sparky said:
I think we are all aware of that and if I recall that is not the issue quogueelectric had. :smile:
480sparky said:
I believe he got a shock from a GFCI protected circuit.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
It is correct that no circuit EGC is required for a GFCI device to operate, nor for the integral test button to work. However, I would like to add that the electrical supply system itself must have a grounded circuit conductor, such as our ever-popular neutral, for it to work.
The reason the integral test button works with no EGC, but plug-in testers don't, is that the built-in test circuit has electrical access to the grounded conductor ahead of the CT ring for connection of the resistor that simulates human contact to the ungrounded condcutor.
Making that same connection after the ring is simply seen by the GFCI as normal line-to-neutral current, since that current travels equally on both circuit conductors, and thus does not generate a voltage on the ring's sensing coil, so the GFCI does not trip.
If one were to disassemble a GFCI receptacle, it would be obvious that there is no electrical connection between the circuitry and the EGC. Besides, if a connection to the system EGC was required, how on earth could GFCI breakers possibly work?
The reason the integral test button works with no EGC, but plug-in testers don't, is that the built-in test circuit has electrical access to the grounded conductor ahead of the CT ring for connection of the resistor that simulates human contact to the ungrounded condcutor.
Making that same connection after the ring is simply seen by the GFCI as normal line-to-neutral current, since that current travels equally on both circuit conductors, and thus does not generate a voltage on the ring's sensing coil, so the GFCI does not trip.
If one were to disassemble a GFCI receptacle, it would be obvious that there is no electrical connection between the circuitry and the EGC. Besides, if a connection to the system EGC was required, how on earth could GFCI breakers possibly work?
crossman
Senior Member
- Location
- Southeast Texas
LarryFine said:
Depends on what you mean by "to work". A GFCI breaker or receptacle will trip whenever the imbalance through the CT exceeds whatever level the manufacturer has built into the device, and a grounded circuit conductor at the supply is not a prerequisite for this tripping to occur.
mivey
Senior Member
Ok quogue, as one of the manufacturer's pets (I notice Mike Holt is one too) I would like to know the pet cow's beef.
Where did you discuss the issue you had or can you give a review of why the ground is needed for proper operation?
You have been roasted to about medium well so how about some details.
Are you saying without a ground they will not operate properly and/or do not have a low enough fault impedance or what?
By "need a ground" are you talking about connected to the device or ground as in a low impedance path through the earth back to the source ground point?
Where did you discuss the issue you had or can you give a review of why the ground is needed for proper operation?
You have been roasted to about medium well so how about some details.
Are you saying without a ground they will not operate properly and/or do not have a low enough fault impedance or what?
By "need a ground" are you talking about connected to the device or ground as in a low impedance path through the earth back to the source ground point?
dbuckley
Senior Member
- Location
- Canterbury, New Zealand
crossman said:
Whereas what you say is absolutely true, its pretty hard to get a current imbalance without the supply being grounded. In particular, a single fault such as a hot to plumbing touch would not cause any current to flow in the absence of a ground bond somewhere. Such a supply would have two hots and no neutral.
dbuckley said:
Why would the plumbing need to be bonded? Bonding is intentionally creating a ground path. If it's copper or galvanized pipe thoughout, there's going to be a path to ground, even if it occurs at the pipe coming in from the street. A structure with all-metal piping is bound to be grounded, whether effective )or intentional) or not.
I don't understand what you mean by 'two hots and no neutral".
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
What I mean by "to work" is to protect a human being who is in contact with the earth (or other grounded surface) from electrocution due to accidental contact with an energized conductor or equipment.crossman said:
In order for an imbalance of current to occur, and be detected, the difference current must flow from one circuit conductor after the CT to the other conductor before the CT.
Typically, the "after-the-CT" contact is with an energized conductor or equipment. That means that the return pathmust be through the human to the contact with the earth or other grounded surface.
If the circuit has no grounded conductor, the first "fault" will (theoretically) have no effect, just as with the first ground fault in a floating supply, such as you have with a non-grounded Delta service.
So I stand by my statement.
- Location
- Illinois
- Occupation
- retired electrician
If the circuits connected to the ungrounded system have enough capacitance it will be possible to have over 5mA of "ground fault" current on an ungrounded system. In the past, when I have used my solenoid voltage tester, on ungrounded systems many of them would have enough current to ground to move the solenoid. The tester will always trip a GFCI and only sometimes trip a 30mA GFP so I conclude that the current required to operate the solenoid is between 5 and 30 mA.
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